Forming rolls

ABSTRACT

THIS INVENTION IS DIRECTED TO COMPOSITE, BI-METALLIC FORMING ROLLS PRODUCED BY POWDER METALLURGICAL METHODS WHICH ARE USED TO FORM STEEL BARS THE COMPOSITE, BIMETALLIC ROLLS ARE NMADE UP OF A WORKING PART OD CEMENTED TUNGSTEN CARBIDE WHICH IS METALLURGICALLY BOUND TO A CASING MATERIAL OF VARIOUS METALS OR ALLOY COMPOSITIONS.

Oct. 5, 1971 J. M. KROL 3,609,849

FORMING ROLLS Filed April 9, 1969 INVEN'I'OR. JAN 7 K80; BY

United States Patent O 3,609,849 FORMING ROLLS Jan M. Krol, 44 Gramercy Park, New York, N.Y. 10010 Filed Apr. 9, 1969, Ser. No. 814,763 Int. Cl. 1521b 27/02 U.S. Cl. 29-132 9 Claims ABSTRACT OF THE DISCLOSURE This invention is directed to composite, bi-metallic forming rolls produced by powder metallurgical methods which are used to form steel bars The composite, bimetallic rolls are made up of a working part of cemented tungsten carbide which is metallurgically bound to a casing material of various metals or alloy compositions.

BACKGROUND This invention relates generally to bi-metallic forming rolls produced by powder metallurgical methods which are used for forming bars, for example, steel bars.

More particularly, this invention relates to composite bi-metallic forming rolls of hard materials, currently widely used as tool and wearor heat-resistant materials, and steel or other similar strong and ductile alloys which provide a support or casing for the former. Such hard materials comprise carbides of the transition metals of the fourth and sixth groups of the periodic systems. Typical representatives of these metals are tugnten, titanium, tantalum, molybdenum, zirconium and chromium.

Hard metals are usually processed by techniques of powder metallurgy as metal-bonded or cemented products, and generally known as cemented carbides. These carbides usually comprise combinations of carbides such as tungsten carbide, titanium carbide and tantalum carbide with binder metals such as cobalt and nickel. Due to their specific properties, such as high hardness values, high modulus of elasticity, high melting point, high wearreistance and cutting characteristics, cemented carbides, and particularly tungsten carbide, have been used for production of cutting and shearing tools, swaging, drawing, stamping, molding or forming dies and wear-resistant parts. By nature, however, these materials are inherently brittle and not suitable by themselves to function as an entire tool or die for several reasons. For example, such tools made of hard metals are often too brittle and not practicable because of the stresses set up in service, and also because of the excessive expensive involved in making them. p

Casing or supporting alloys into which the cemented carbides are set provide other physical properties that the cemented carbides lack and allow them to function usefully. They include, for example, cemented carbides with high contents of binder metals such as cobalt, nickel and iron or other alloys comprising tungsten, copper, nickel and iron; iron and nickel; and tungsten, copper and nickel.

Heretofore, in rolling and forming operations a ring of cemented tungsten carbide, for example, had to be attached to a high speed steel machine shaft either mechanically or by brazing. Neither of these methods of attachment is satisfactory since the tungsten carbide ring is not properly supported and excessive breakage of the carbide results. The breakage of the brittle carbide under the high speeds at which the machine shaft rotates presents great hazards both to the machine and the machine operator.

A mechanical method of attachment is unsatisfactory in that a complicated series of linkages are necessary to attach the carbide ring to the machine shaft, and the "ice attachment sometimes loosens with wear. This method is also uneconomical in that it requires finely machined steel attachment plates and finely ground surfaces of the carbide rings to assure good contact.

Brazing the carbide ring to a steel shaft also has disadvantages. Even if a good joint is obtained between the steel shaft and the cemented carbide, there is a danger of cracking because of the difference in the coefficients of thermal expansion between the steel shaft, the carbide and the brazing material. It also requires fine machining and grinding to assure good contact between the shaft and the carbide ring.

Neither method of attachment allows the use of a cemented carbide of maximum wear resistance. In a cemented carbide the strength of the resultant cemented carbide is a function of the mount of binder metal, such as cobalt, which is used. As the amount of binder metal increases the strength of the carbide increases with a resultant decrease in wear resistance and brittleness. Because of the excessive breakage problems caused by the prior methods of attachment, the strength of the cemented carbides used had to be increased with the use of higher levels of cobalt with the resultant sacrifice of wear resistance.

In this connection, cemented carbides which have less than 16% cobalt are generally known as low cobalt carbides as opposed to cemented carbides with over 16% cobalt which are known as high cobalt carbides. Obviously the low cobalt carbides are more brittle and have greater wear resistance while the high cobalt carbides have greater strength.

THE INVENTION It is therefore an object of this invention to provide a forming roll which has a more wear resistant tungsten carbide working surface.

It is another object of this invention to provide a bimetallic forming roll that is safer, more economical, and easier to attach to a high speed machine shaft.

Therefore, according to this invention there is provided a bi-metallic forming roll compirsing a working part of cemented carbide which comprises a mixture of carbide of a metal, such as tungsten, titanium, tantalum, molybdenum, zirconium or chromium with the balance being 3 to 16% binder metal, such as cobalt or nickel, and a casing of cemented carbide with 1660% binder metal. The casing may also be made of various alloys including, for example; to tungsten, 3 to 10% copper, 3 to 10% nickel to which 3 to 10% iron can be added, 50 to 70% iron and 30 to 50% nickel; and 20 to 30% nickel, 12 to 18% cobalt and 40 to 55% iron. (All percentages throughout this specification are by weight.)

In the forming roll of this invention the working part provides the wear resistance, while the casing material, which is metallurgically bonded to the working part of the cemented carbide, supplies the other requirements expected in a good steel forming roll, namely, good physical properties, toughness, high modulus of elasticity, proper hardness, fatigue resistance, a proper coefficient of thermal expansion and ease of machinability.

For a more detailed description of the invention, reference should be made to the drawings.

FIG. 1 is a perspective view showing two forming rolls according to the invention attached to a machine shaft, forming and reducing a steel bar.

FIG. 2 is a partial cross-section view of the forming roll of FIG. 1 which also shows the method of attachment to the machine shaft.

FIG. 3 is a perspective cross-section of the forming roll.

Referring to FIG. 3, the forming roll comprises a grooved cemented carbide wear-resistant working part which is a mixture of 84 to 97% tungsten carbide and 3 to 16% cobalt. The casing 11 comprises a mixture of 40 to 84% tungsten carbide with 16 to 60% cobalt or various other alloys can be used.

Alloys that have been found useful for the casing are: 80 to 95% tungsten, 3 to 10% copper, 3 to 10% nickel to which 3 to 10% iron can be added; 50 to 70% iron and 30 to 50% nickel; 20 to 30% nickel, 12. to 18% cobalt and 40 to 55% iron; and 30 to 40% chromium and 60 to 70% iron.

FIGS. 1 and 2 show a steel bar 12 being reduced and formed by the working part 10 of the forming rolls. The forming roll is mounted on a shaft 13 which has a locking disc 14 secured thereto. The roll is provided with slots which engage dogs extending radially across the face of the disc. The roll is retained in engagement with the disc by a locking disc 14a and a retaining nut 15 which is screwed onto the shaft 13. This connection to the machine shaft is much simpler than the prior art because only simple locking devices are used and the surfaces of the locking devices and the bi-metallic rolls can be machined by conventional methods. The connection is also more secure.

The forming rolls of this invention may be made by various powder metallurgical methods which will be described below. Essentially, the powder metallurgical methods of production may be either a one step or a two step operation. The one step operation may consist of either hot pressing or cold pressing and sintering or infiltration.

In the hot pressing operation, hard metal inserts are placed in a prepared form for molding, for example, of graphite which has inserts for the grooved working part 10. A layer of powdered tungsten carbide blended with 16 to 60% cobalt depending upon the desired application is first placed in the mold, then a layer of powdered tungsten carbide blended with 3 to 16% cobalt is placed in the mold around the working surface insert to conform the shape of the working part 10 shown in FIG. 3. On top of this another layer of tungsten carbide blended with 16 to 60% of cobalt is placed. Graphite plungers are then placed on top of the resulting powdered metal sandwich. The mold is then heated to 2000 to 2800 F. under a total pressure of 1 to 3 tons and maintained at these temperatures and pressure until full density of the final product is obtained. The pressing operations are carried out on conventional equipment. After the mold is removed the result is a forming roll with a low cobalt cemented carbide high wear-resistant working part 10 within a high cobalt casing alloy 11. The hot pressing operation described above can also be performed with the substitution of various alloy powders for the casing 11.

Various alloy powders, which have been found useful in the process for the casing, are: 80 to 95% tungsten, 3 to 10% copper, 3 to 10% nickel to which 3 to 10% iron can be added; and 50 to 70% iron and 30 to 50% nickel. These alloys can be used under generally the same time, temperature and pressure conditions as the high cobalt cemented carbide.

The forming rolls can also be infiltrated by cobalt or other metals or alloys if the density of the roll is insuflicient or if greater density is desired. Infiltration is a process in which the pores of the roll are filled with a metal or alloy which has a lower melting point than the roll.

Forming rolls can also be made by cold pressing the low cobalt tungsten carbide powder mixture and the high cobalt pie-alloyed tungsten carbide powder mixture described above. The sandwich should be cold pressed at pressures of about 30 tons per square inch and then sintered at a temperature of about 2000 to 2800 F. while under a total pressure of 1 to 3 tons pressure until full density is obtained.

The various other alloyed powders substituted in the hot pressing method for the high cobalt tungsten carbide mixture can also be used in the cold pressing method using generally the same time, temperatures and pressures.

A forming roll made by the cold pressing and sintering method can also be infiltrated by cobalt or other metal or alloys if the resultant product has insufficient density or if greater density is required.

Infiltration after either hot pressing or cold pressing and sintering is done at a temperature sufiicient to melt the metal or the alloy and at a time sufficient for the required penetration.

The essential requisite of either operation is the resultant metallurgical bond between the working part 10 and the casing 11.

The novel bi-metallic forming roll can also be formed in a two step method. In a two step method a cemented tungsten carbide ring with 3 to 16% cobalt is produced by any conventional powder metallurgical method. This preformed ring does not require any fine grinding or other finishing operations. The preformed ring is hot pressed in a mold to obtain the configuration shown in FIG. 3 using an alloy powder mixture comprising 20 to 30% nickel, 12 to 18% cobalt, and 40 to 55% iron, at a total pressure of 1 to 6 tons at 2100 to 2200 F. for approximately 20 minutes to obtain full density. To this alloy powder various carbide forming elements, such as molybdenum, chromium, tungsten, tantalum or vanadium can be added in amounts of 1 to 20%. The use of about 10% of molybdenum has been found to be especially useful. -In producing the forming roll by this process, the hot pressing temperature must produce a liquid face between the alloy powder and cemented carbide ring to allow diffusion into the cemented carbide ring forming a metallurgical bond. Furthermore, the alloy powder must be of a composition that allows a liquid face to be formed at moderate temperatures of 2000 to 2300" F. The process described above has been found to be the preferred and simplest method for producing the bi-metallic forming roll and produces a useable finished product.

In the above process, alloy powders of the following compositions can also be effectively used for the casing: 40 to 60% iron and 40 to 60% nickel; and to tungsten with the remainder being copper and nickel. Again the times, temperatures, and pressures are within the described ranges.

The forming roll can also be produced by another two step method of cold pressing followed by sintering and infiltration. Again, a preformed cemented tungsten carbide ring containing 3 to 16% cobalt, which has been produced by one of the conventional powder metallurgical methods, is used. A metal powder or alloy described previously is cold pressed to a uniform density around the preformed ring under a pressure of up to 30 tons per square inch to obtain a configuration exhibited by FIG. 3. The resulting material is then sintered and infiltrated by an appropriate metal alloy. It has been found that the sintering and the infiltaration can be carried on either separately or simultaneously. In either event, the operation must be carried on at such a temperature, pressure and time that will allow the casing alloy to diffuse into the tungsten carbide to produce a metallurgical bond between the two materials.

It has been found that a preferred method is to cold press a mixture of iron powder with 30 to 40% of chromium around the preformed ring at a pressure of 30 tons per square inch to obtain uniform density. This is then sintered and simultaneously infiltrated with copper at 2050 F. for approximately 30 minutes or with Monel metal at 2150 F. for approximately 30 minutes or with an alloy of 10 to 20% nickel, 10 to 30% zinc and the balance being copper at 1900 to 2100 F. for approximately 30 minutes. Other proper copper alloys can also be used. The infiltration can be followed by pressing under 1 to 6 tons total pressure to produce a denser forming roll.

Trace amounts of additional elements may be present in the alloy powders described herein and are encompassed by this invention. Examples of these trace elements are carbon, boron and silicon.

The following examples are given by way of illustration.

Example I A satisfactory six inch diameter forming roll was produced by hot pressing an alloy powder of 10% molybdenum, 49% iron, 22% nickel, 16% cobalt, 1.5% chromium with traces of carbon, boron and silicon around a preformed tungsten carbide ring which contained 16% cobalt. The hot pressing was carried out at a temperature of 2170 F. under a total pressure of 4 tons for 20 minutes.

Example 11 A satisfactory six inch diameter roll was produced by cold pressing an alloy powder of 70% iron and 30% chromium around a preformed tungsten carbide ring which contained 13% cobalt at a pressure of 20 tons per square inch. The roll was then simultaneously sintered and infiltrated with copper at 2050 to 2100 F. for 30 minutes.

What is claimed is:

1. A bi-metallic forming roll comprising a working part of cemented carbide and a casing of a metal or an alloy adapted to give strength and rigidity to the roll, said casing material having a coefiicient of thermal expansion similar to that of the cemented carbide and where the working part and the casing are metallurgically bonded together.

2. A bi-metallic forming roll according to claim 1 wherein the casing comprises approximately 40 to 55% iron, approximately 12 to 18% cobalt, and approximately 20 to 30% nickel.

3. A bi-metallic roll according to claim 1 wherein the casing comprises approximately 40 to 55 iron, approximately 12 to 18% cobalt, approximately 20 to 30% nickel, and approximately 5 to 15% molybdenum.

4. A bi-metallic roll according to claim 1 wherein the casing comprises approximately 60 to 70% iron and approximately 30 to chromium.

5. A bi-metallic roll according to claim 1 wherein the casing comprises tungsten carbide and approximately 16 to cobalt.

6. A bi-metallic roll according to claim 1 wherein the working part comprises one or more carbides of metals selected from the group consisting of tungsten, titanium, tantalum, molybdenum, zirconium and chromium mixed with approximately 3 to 16% of binder metal selected from the group consisting of nickel, cobalt and iron.

7. A bi-metallic roll according to claim 1 wherein the cemented carbide working part comprises tungsten carbide and approximately 3 to 16% cobalt.

8. A bi-metallic roll according to claim 1 which has been formed by powder metallurgical methods.

9. A bi-metallic forming roll comprising a cemented carbide working part and a casing made of a metal or an alloy which will produce a liquid face to allow diffusion into a preformed cemented carbide ring.

References Cited UNITED STATES PATENTS 2,167,544 7/1939 De Bats et al. 1,993,598 3/1935 De Bats. 2,950,097 8/1960 Tohir 29129 X 2,988,803 6/1961 Mohn 29129 X 3,432,902 3/1969 Rackoff et a1 29125 3,435,499 4/1969 Rackoff et al. 29l25 3,456,931 7/1969 Ermenc et a1 29-132 X 3,503,241 3/1970 Vom Dorp et al. 29-125 X ALFRED R. GUEST, Primary Examiner 

